FLC TAXIED THEIR ACFT ONTO ACTIVE RWY WITHOUT RECEIVING AN ATC CLRNC.

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I WAS THE CAPT TAXIING THE ACFT AT SEA. WE WERE TOLD TO TAXI TO RWY 34R AT TXWY Q AND HOLD SHORT. TWR GAVE US INSTRUCTIONS TO TAXI ACROSS RWY 34R AT TXWY Q AND HOLD SHORT RWY 34L. THE FO AND I MISUNDERSTOOD THE TWR AND WE POSITIONED INTO RWY 34L. THE FO READ BACK INSTRUCTIONS TO 'TAXI INTO POS AND HOLD ON RWY 34L' AND WE BOTH COMMUNICATED THOSE INSTRUCTIONS AMONGST OURSELVES. I CHKED TO SEE THAT FINAL WAS CLR AND CALLED FOR THE 'BELOW THE LINE' CHKLIST. ONCE WE WERE ALIGNED ON THE RWY; TWR TOLD US THAT WE WERE NOT CLR TO TAXI ONTO RWY 34L AND TO EXIT ON THE W SIDE. BOTH THE FO AND I WERE SURPRISED AT THE CALL FROM TWR HAVING REITERATED THAT WE UNDERSTOOD WE WERE TO POS AND HOLD. I BELIEVE THAT THE FO READ THIS CLRNC BACK INCORRECTLY. I USUALLY ALWAYS CONFIRM THE CLRNC AND WAS SURE THAT IS WHAT WE HEARD. APPARENTLY WE HEARD INCORRECTLY. THERE WERE NO OTHER ACFT AT ALL IN THE AREA OR ON FINAL FOR OUR RWY. WE WERE SUPPOSED TO HOLD SHORT TO WAIT FOR WAKE TURB FROM A B777 DEP OFF THE OTHER RWY (RWY 34R). SUPPLEMENTAL INFO FROM ACN 462925: HAD WRONG TWR FREQ IN RADIO INITIALLY. AFTER 30 SECONDS; FIXED THE PROB. CTLR CHASTISED US FOR NOT RESPONDING. APPARENTLY TOLD US TO CROSS RWY 34R AT TXWY Q; HOLD SHORT RWY 34L. NO OTHER INCIDENT BECAUSE OF THIS EXCEPT FOR A CALL TO OUR CHIEF PLT FROM THE TWR. TWR DID NOT CORRECT THE READBACK; WHICH WOULD HAVE PREVENTED THIS SIT.